Anthos/Cloud Service Mesh - How to Set Ingress Gateway Log Format to JSON?

Question

I provisioned a managed Anthos/Cloud Service Mesh and set the sidecar access logs to JSON using the MeshConfig.AccessLogEncoding property. Now, I am trying to configure the ingress gateway logs to use the JSON format as well.

I managed to achieve it by manually editing the ingress gateway pod and adding the --log_as_json container argument:

apiVersion: v1
kind: Pod
metadata:
...
spec:
  containers:
    - args:
        - proxy
        - router
        - --domain
        - $(POD_NAMESPACE).svc.cluster.local
        - --proxyLogLevel=warning
        - --proxyComponentLogLevel=misc:error
        - --log_output_level=default:info
        - --stsPort=15463
        - --log_as_json
      env:
        - name: JWT_POLICY
          value: third-party-jwt
...

This is a sample log entry in Cloud Logging:

{
  "insertId": "...",
  "jsonPayload": {
    "level": "info",
    "msg": "connected to upstream XDS server: meshconfig.googleapis.com:443",
    "scope": "xdsproxy"
  },
  "labels": {
    "compute.googleapis.com/resource_name": "...",
    "k8s-pod/app": "...",
    "k8s-pod/istio": "ingressgateway",
    "k8s-pod/pod-template-hash": "5dd6f69c5f",
    "k8s-pod/service_istio_io/canonical-name": "...",
    "k8s-pod/service_istio_io/canonical-revision": "latest"
  },
  "logName": "...",
  "receiveTimestamp": "...",
  "resource": {
    "labels": {
      "cluster_name": "...",
      "container_name": "istio-proxy",
      "location": "...",
      "namespace_name": "...",
      "pod_name": "...",
      "project_id": "..."
    },
    "type": "k8s_container"
  },
  "severity": "INFO",
  "timestamp": "..."
}

However, ingress gateway deployment manifests are auto-injected by ASM by setting the inject.istio.io/templates: gateway annotation, and the --log_as_json container argument is not configured by the template:

apiVersion: apps/v1
kind: Deployment
…
  template:
    metadata:
      annotations:
        # This is required to tell Anthos Service Mesh to inject the gateway with the
        # required configuration.
        inject.istio.io/templates: gateway
     …
    spec:
      containers:
      - name: istio-proxy
        image: auto # The image will automatically update each time the pod starts.

How can I instruct Anthos/Cloud Service Mesh to include --log_as_json in the container arguments when injecting the gateway template?